Lecture 15: Transport of oxygen in the blood

Question 1

What is respiration in terms of respiratory physiol?

Answer 1

The process of oxygen diffusion through the alveoli into the blood

Question 2

What are factors that regulate the movement of gas across the resp. surface?

Answer 2

1. Area 2. Thickness of the tissue 3. Partial pressure differential across tissue 4. Solubility of gas in blood 5. Molecular weight of gas

Question 3

What is the implication for the factors that regulate the movement of gas across the resp. surface?

Answer 3

These are the same factors that can change in diseases states. Reduced gas exchange; decreased O2 and increased CO2

Question 4

What are some notable features about the lungs surface area?

Answer 4

~300m alveoli, at 0.3mm diam = surface area of 50-100m2 and 4L volume i.e extremely high area to volume ratio

Question 5

What creates the thickness of the tissue?

Answer 5

• Surfactant - Epithelium - Interstitium - Basement membrane - Endothelial cell ~0.5um thick between air and blood!!!!

Question 6

What is the risk the thickness of the tissue?

Answer 6

Pulmonary hypertension results in increased distance which compromises gas exchange

Question 7

What is the partial pressure across the tissue of oxygen and CO2?

Answer 7

The partial pressure of oxygen is 100mmHg in the alveoli and around 40mmHg in the tissue = delta 60mmHg of driving force into the tissue CO2 is around 46mmHg in the tissue and 40mmHg in the alveoli, delta 6mmHg (driving force) Oxygen partial pressure driving force is 10x greater that CO2, yet other factors create equal drive

Question 8

Discuss solubility of gas in blood and molecular weight of gas in oxygen respiration:

Answer 8

Solubility more important than MWt of gas. CO2 is 25 times more soluble in blood than oxygen…..BUT…… release time of CO2 from HB is slower than O2 So on movement of both gases across alveolar membrane are balanced

Question 9

Whats another risk of the thin diffusion distance?

Answer 9

Increased chance of infection but lung developed to deal with it

Question 10

Describe this graph;

Answer 10

N2O and O2 are both perfusion limited (inc. blood through alveoli will change these curves) CO is diffusion limited (long bonding time) - Thus an increase in concentration will increase diffusion

Question 11

How is oxygen transported in blood?

Answer 11

1. Binds with Hb (most imp) 2. Dissolves in solution (Plasma: Dictated by if youre breathing air or pure O2 (Dep. on conc. gradient).

Question 12

What is the carrying capacity of blood for oxygen?

Answer 12

200mL of oxygen per litre of blood 1g of Hb can transport 1.39mL of oxygen (aq) when fully saturated

Question 13

Describe how the Hb molecule binds oxygen;

Answer 13

Co-operative binding Structure: - Two alpha and beta polypeptide chains - each contains a haem moiety - Allosteric effect = Cooperative binding Changes affinity for O2 as different n. O2 bound. Once first binding is bound, heame twists and second site is exposed etc till all sites bound

Question 14

What sort of relationship is the oxygen dissociation curve?

Answer 14

Sigmoidal relationship due to cooperative binding = Each bound O2 increases affinity / likelihood for next )2 binding

Question 15

Describe three important parts of the oxygen dissociation curve:

Answer 15

• Systemic veins have ~75% oxygen saturation of Hb and at this point theres lower affinity for O2 at lower PO2s - Systemic arteries have ~99% oxygen saturation of Hb and at this point theres higher affinity for O2 at higher PO2s. - Difference between these two points = Percent of O2 unloaded by Hb to tissues

Question 16

Describe the implication of lower and higher affinity oxygen points on the oxygen dissociation curve:

Answer 16

• Lower affinity for O2 at lower PO2 = Encourages O2 RELEASE at TISSUES - Higher affinity for O2 at higher PO2 = Encourages O2 UPTAKE at LUNGS

Question 17

Describe the name of Hb in various oxygen bound states?

Answer 17

Hb4O2 = Deoxyhaemoglobin Hb4O4 = Partially saturated Hb4O6 = Oxyhaemoglobin Hb4O8 = Fully saturated

Question 18

Whats the equation of CO2 diffusion in blood?

Answer 18

CO2 + H2O H2CO3 H + HCO3 Law of mass action will determine the direction of this chemical reaction

Question 19

What happens to Hb in an acidic evnironment?

Answer 19

In an acidic environment Hb less affinity for O2: At tissues: More CO2, lower pH, So O2 is released At lungs: Less CO2, higher pH, so O2 is taken up Hb4O8 + H+ Hb4 + 4O2 -> To tissues

Question 20

What does this oxygen dissociation curve represent?

Answer 20

It demonstrates that at pure oxygen (600mmHg vs 100) the O2 combined with Hb i.e Hb saturation increases minimally. Whilst the dissolved O2 increase is more pronounced, increasing the overall O2

Question 21

What does this oxygen dissociation curve represent?

Answer 21

Anemia reduced the oxygen content of blood even if saturation was 100%. i.e in disease that impacts Hb, can change blood oxygen content.

Question 22

What is the bohr shift?

Answer 22

It is the right shift of the oxygen dissociation curve generated when theres increased CO2, hydrogen ions, temperature, DPG. i.e at tissues Bohr Shift: For a given PO2, lower affinity of HB for O2 so more oxygen is released

Question 23

What left shifts the oxygen dissociation curve?

Answer 23

Decreased CO2, H+, Temperature, DPG i.e at lungs Oxygen binds much easier here.

Question 24

How do globins change the oxygen dissociation curve?

Answer 24

Myoglobin left shifts the curve Fetal heamoglobin is also left shifted, helps movement of oxygen across the placenta to the feotus.

Question 25

Why do we need erythrocytes?

Answer 25

• Encapsulates a high conc. of Hb (dec. blood viscocity) - Provides an environment for DPG (diphosphoglycerate) (Enhances O2 downloading at tissues) - Encapsulates and concentrates carbonic anhydrase (Essential for CO2 transport) - Prevents Hb loss via filtration in kidneys - Concave shape helps passage thru tight spaces

Question 26

What is DPG?

Answer 26

Diphosphoglycerate is an intermediate of glycolysis in the RBC Binds Hb and reduces Hb affinity for Oxyge

Question 27

What changes DPG levels?

Answer 27

In low PaO2 environments i.e tissues metabolism of DPG is slowed and it can bind Hb Fetal Hb has lower affinity for DPG

Question 28

Write some notes on myoglobin?

Answer 28

One O2 molecule only, pH insensitive, O2 store, Fully saturated before Hb starts to bind O2.